Stripline circulator biased by a plurality of small pole pieces

ABSTRACT

A plurality of small magnets or pole pieces are disposed in opposed relation with a line conductor vacuum-deposited upon one surface of a disk-shaped magnetic medium so that the external magnetic field may be vertically applied to the line conductor. The frequency band characteristic as well as the backward loss characteristic may be improved.

United States Patent Miura et al.

STRIPLINE CIRCULATOR BIASED BY A PLURALITY OF SMALL POLE PIECES Inventors: Taro Miura, Tokyo; Kiichi Nakamura; Tadashi Hashimoto, both of lchikawa, all of Japan Assignee: T.D.K. Electronics Company, Ltd.,

I Tokyo, Japan I Filed: June 18, 1971 Appl. No.: 154,422

Foreign Application Priority Data June 30, 1970 Japan ..45/57578 11.5. C1. ..333/1.1, 333/84 M rm. c1. ..H0lp 1/32, HOlp 5/12 Field of Search ..333 1.1, 24.1, 24.2

POLE PIECES Germany ..333/l.l

Primary Examiner-Paul L. Gensler Attorney-Milton J. Wayne et al.

[57] ABSTRACT A plurality of small magnets or pole pieces are disposed in opposed relation with a line conductor vacuum-deposited upon one surface of a disk-shaped magnetic medium so that the external magnetic field may be vertically applied to the line conductor. The frequency band characteristic as well as the backward loss characteristic may be improved.

3 Claims, 17 Drawing Figures FERRITE MATERIAL l4 STRIPLINE J CONDUCTOR PATENTEDAPM 1975 7 5, 23

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SHEET 3 BF 9 G13 552m ow ON ow on Q p.14 EOEQ PATENT 1915 3.7251323 SHEET 5 BF 9 PATENTEDAPRB I975 SHEET 7 [IF 9 wDOwmm mmOJ PATENTEDAPR3 I975 SHEET 9 BF 9 T18 Szwnowwt STRIPLINE CIRCULATOR BIASED BY A PLURALITY OF SMALL POLE PIECES BACKGROUND OF THE INVENTION The present invention relates to a circulator which is one element of a microwave circuit, and more particularly to an improvement of a stripline circulator.

In microwave circuits, circulators are widely used in duplexers, separation networks, parametric amplifiers, modulators and the like, and recently have come to be used in television transmission techniques. Furthermore, the circulators are now operated not only in the microwave region but also in the light wave region.

Various types of circulators have been developed, and they are generally divided into two types, one being the waveguide circulators and the other, the coaxial circulators. The coaxial circulators are also called stripline circulators and are used widely in various fields because of their unusual compactness in size, light weight and a broad operating band. In general, the construction of a typical stripline circulator is such that a line conductor having Y-shaped branches or striplines, Z-shaped or four striplines or the like is deposited in a vacuum upon the upper surface of a magnetic medium such as ferrite while a ground conductor is deposited in a vacuum upon the undersurface thereof, the external magnetic field being applied vertically to the line conductor.

When the stripline circulators of the type described are used in the microwave circuits, it is generally required that they have the characteristics shown in Table 1 given below.

TABLE 1 bandwidth 7 insertion loss backward loss However, in the prior art universal type stripline circulators, when the bandwidth becomes greater than percent, the backward loss or isolation is of the order of 20 dB at the most so that a few circulators must be connected in cascade to attain a desired backward loss, but the insertion loss is increased in proportion to the number of circulators. Therefore when the stripline circulators are employed for example in a parametric amplifier, their function is greatly diminished. Even when a backward loss greater than 40 dB is obtained by the cascade connection of the circulators, undesired phenomena such a displacement or drift of center frequency, reduction in bandwidth, increase in insertion loss and the like are observed because the individual circulators do not match and interact with each other.

v To overcome these problems, there has been proposed an improvement in which a magnetic medium, which is generally of ferrite materials, is uniformly magnetized so that the desired characteristics as shown in Table I may be attained by a single stripline circulator, but this improvement has been found unsatisfactory because the maximum backward loss attainable is of the order of 35 dB.

SUMMARY OF THE INVENTION The present invention has for its object to provide an improved stripline circulator in which the magnetic fields produced by a plurality of magnets are vertically applied to a line conductor.

The inventors made extensive studies and experiments with stripline circulators, and found out that when a magnet which is disposed in opposed relation with the line conductor is made of a plurality of small magnet elements or pole pieces, a stripline circulator may be operated over a wide band with a desired degree of backward loss without any appreciable increase in insertion loss.

According to a preferred embodiment of the present invention, at the. center of the space defined in an airtight yoke is disposed a ferrite magnetic medium upon the upper surface of which is deposited in a vacuum a line conductor consisting of a circular conductor portion and three branched striplines and upon the undersurface of which is also deposited in a vacuum a ground conductor. A pair of magnets sandwiches this magnetic medium with the magnet disposed in opposed relation with the 'line conductor comprising four pole pieces which are disposed in opposed relation with the circular conductor portion and the-three striplines respecgreater than 40 dB, the bandwidth,

tively. In a single stripline circulator in accordance with the present invention, the backward loss becomes 31 percent and the insertion loss less than 0.4 dB.

The present invention will become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION FIG. la is a sectional view of a typical prior art stripline circulator;

FIG. lb is a sectional view taken along the line A- A of FIG. la;

FIG. 2 is a circuit diagram of a parametric amplifier employing the stripline circulators of the type shown in FIGS. 1a and b;

FIG. 3a is a sectional view of a stripline circulator in accordance with the present invention;

FIG. 3b is a top view of a magnet disposed in opposed relation with a line conductor in the circulator shown in FIG. 3a;

FIG. 30 is a side view thereof;

FIG. 4 is a view for explanation of the relative positions of the magnet element or pole pieces shown in FIGS. 3b and 3c withrespect to the line conductor;

FIGS. 5-7 are views illustrating some variations of the magnet shown in FIGS. 3b and 3c both in shape and position;

FIG. 8 is a graph illustrating the relationship between the frequency and loss of the prior art stripline circulator of the type shown in FIG. 1;

FIG. 9 is a graph illustrating the relationship between the frequency and loss of the stripline circulator in ac.- cord with the present invention shown in FIG. 3a; and

FIGS. 10-14 are graphs also illustrating the relationship between the frequency and loss of the variations shown in FIGS. 5-7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an airtight yoke l is provided with another yoke 2, which is fixed to the upper portion of the-airtight yoke 1 and has a magnet 3 fixed to the undersurface of the yoke 2 by holding elements (not labeled). Another magnet 4 is fixed to the lower portion of the airtight yoke l in opposed relation with the magnet 3. These magnets 3 and 4 are generally of barium ferrite, and a magnetic medium 5, which is generally of ferrite, is interposed between the upper and lower magnets 3 and 4. A line conductor consisting of a circular conductor portion 6 and three branched striplines 7,8 and 9 is deposited upon the upper surface of the magnetic medium 5 while a ground or base conductor 11 is deposited in vacuum upon the undersurface thereof. Three coaxial connectors 12, 13 and 14 are fixed to the wall of the airtight yoke 1 in alignment with the three striplines 7, 8 and 9 respectively as the terminals thereof. A grounding conductor 15 is disposed around the lower magnet 4. The electromagnetic energy put into the circulator from the terminal 12 is taken out from the terminal 13 without leaking from the terminal 14. The electromagnet energy put into the circulator from the terminal 13 is transmitted only to the terminal 14. Thus the circulator is a non-reversible circuit in which the electromagnetic energy is transmitted from one terminal to another in a circulating manner.

FIG. 8 shows the frequency-loss curves of the stripline circulator shown in FIG. 1. The ferrite magnetic medium 5 was 15 mm in diameter and 1.7 mm in thickness; the circulator conductor portion 6, 8 mm in diameter; and each of the striplines 7, 8 and 9, 1.7 mm in width. The magnetic field of l,350 0e was applied vertically to the line conductor 10. In FIG. 8, the backward loss curve is designated by A, and the forward loss curve or insertion loss curve by B. A bandwidth is indicated by Af/f, and numbers with lead lines indicating the frequencies at which the measurements were made. It is seen that in the striplinecirculator of the type shown in FIG. 1, the backward loss is 30 dB at the most when the bandwidth is 30 percent.

FIG. 2 shows a parametric amplifier 30 employing the stripline circulators 31 32 and 33 of the type shown in FIG. 1, a reception antenna 34, and a pump source 35. The signal intercepted by the antenna 34 is transmitted in the order as indicated by the numerals 36 37-* 39* 40, amplified by the parametric amplifier 30 and transmitted to the output terminal 43 along the transmission line 41 42 43. In this case, if the circulator 31 is not inserted and the backward loss of the circulator 32 is not satisfactory, a fraction of the signal amplified by the amplifier 30 is transmitted backward to the antenna 34 through the transmission line 40 39 and then reflected back to the amplifier 30 through the line 39 40, so that the operation becomes unstable. When the circulator 31 is inserted, the signal leaked on the line 39 is absorbed into an absorbing resistor connected to the terminal 38 of the circulator 31 so that the leaked signal may be prevented from going to the antenna A. The same is true for the circulator33 so that an absorbing resistor 46 is connected to the terminal 44.v

As described above, when the backward loss obtained by one circulator is not sufficient, a few circulators are cascade-connected to increase the backward loss, but such undesirable phenomenon as described above is observed.

A preferred embodiment of a stripline circulator of the present invention is shown in FIG. 3a and is substantially similar in construction to the prior art circulator shown in FIG. 1 except that a plurality of magnets or pole pieces are employed instead of the single magnet 3. That is,.as shown in FIGS. 3b and c, the magnet 3 comprises four pole pieces 16,17, 18 and 19, and as best shown in FIG. 4, the pole pieces 16 is disposed in opposed relation with the circular conductor portion 6 of the line conductor 10; and the three pole pieces 17, 18and 19 are disposed in opposed relation with the tree striplines 7, 8 and 9 respectively.

In FIG. 9 are shown the frequency'loss curves of the stripline circulator shown in FIG. 3a and provided with the magnet 3 comprising the pole pieces 16, 17,18 and 19 arranged as shown in FIG. 4. The backward loss is indicated by A while the forward loss by B. The dimensions of the magnetic medium 5 and the stripline conductor 10 deposited thereupon and the magnitude of the magnetic field applied were .the same as those of FIG. 8. Each pole pieces was 5 mm in diameter and 3 mm in thickness.

It is seen that in one stripline circulator the bandwidth in which the backward loss is greater than 40 dB is 31 percent while the forward loss or insertion loss within this bandwidth is maintained less than 0.4 dB.

FIGS. 10-14 show the relationships between the frequency and loss when the shapes and arrangement of the pole pieces of the magnet 3 and the method of applying the magnetic field were varied so that the un de-rlying principle of thepresent invention may be fully understood'The backward loss curves are designated by A while the forward loss curves by B. The dimensionsof the pole pieces, the magnetic medium and the stripline conductor were the same as those of FIGS. 8 and 9. More particularly, the graph shown in FIG. 10 indicates the loss curves when the magnetic medium was magnetized only by the center pole piece 16 of the magnet'3 which was arranged as shown in FIG. 4. The

graph shown inFIG. 11 indicates the loss curves when the magnetic medium was magnetized by the peripheral pole pieces 17, 18 and 19 of the magnet 3 which was arranged as shown in FIG. 4. The graph shown in FIG. 12 corresponds to the FIG. 5 variation and indicates the loss curves when the magnet 3 comprises pole pieces 20, 21 and 22 that are so arranged'as to be opposed only to the circular conductor portion 6 of the line conductor 10 as shown in FIG. 5. The graph shown in FIG. 13 corresponds to the FIG. 6 variation and indicates the loss curves when the magnet 3 comprises a triangle pole piece 23 that is so placed that the three vertexes of the triangle were opposed to the striplines 7, 8 and 9 respectively as shown in FIG. 6. The graph shown in FIG. 14 corresponds to the FIG. 7 variation and indicates the loss curves when the pole pieces 17,18 and 19 were rotated through an angle of from the positions shown in FIG. 4 to the positions shown in FIG. 7. that is, the pole pieces 17, 18 and 19 applied the magnetic fields to the portions intermediate the striplines 7, 8 and 9.

pole pieces alone but by the synergistic effect of all These experimental results may be summarized as shown in Table 2 below.

TABLE 2 bandwidth maximum 5 and their respective backward loss backward FIGS. more than greater than greater than loss 20 dB 30 dB 40 dB (dB) 8 51 3| 35 9 48 36 31 5O l0 l4 35 11 46 a 2 45 12 38 24 13 49 32 It is difficult to theoretically analyze why such better frequency characteristics or loss curves are obtained, but the experimental data may be summarized as follows:

1. Better results are obtained when the diameter of the magnetic medium was about 2 times that of the circular conductor portion of the line conductor; I

2. The most intense portion of the magnetic field must be on the line conductor;

3. The characteristics as shown in FIG. 9 are not obtained from the central pole piece or the peripheral pole pieces;

4. The function of the peripheral pole pieces is not limited to the impedance matching; and t 5. No satisfactory result will be attained if the magnetization is directed only to the electromagnetic field immediately below the circular conductor portion.

The present invention has been described so far by reference to the three-branch stripline circulator, but it is understood that the present invention may be also applied to other types of stripline circulators such as four-branch circulators.

What is claimed is:

l. A stripline circulator characterized in that a pair of magnets are disposed in an airtight yoke in such a manner that the poles thereof are opposed to each other, between said pair of magnets is interposed a ferrite material upon the upper surface of which is deposited in vacuum a line conductor consisting of a circular conductor portion and a plurality of striplines and upon the undersurface of which is deposited in vacuum a ground conductor, and one of said pair of magnets in opposed relation with said line conductor comprises a plurality of small pole pieces.

2. A stripline circulator as set forth in claim 1 wherein said plurality of small pole pieces are so disposed as to oppose the circular conductor portion and said plurality of striplines respectively.

3. A stripline circulator as set forth in claim 2 wherein said plurality of striplines of said stripline conductor comprises three striplines, and said plurality of conductor comprises four pole pieces.

small pole pieces in opposed relation with said stripline 

2. A stripline circulator as set forth In claim 1 wherein said plurality of small pole pieces are so disposed as to oppose the circular conductor portion and said plurality of striplines respectively.
 3. A stripline circulator as set forth in claim 2 wherein said plurality of striplines of said stripline conductor comprises three striplines, and said plurality of small pole pieces in opposed relation with said stripline conductor comprises four pole pieces. 